Hard-facing alloys having improved crack resistance

ABSTRACT

Weld deposit compositions with improved crack resistance, improved wear resistance, and improved hardness are provided by controlling matrix grain size and balancing Titanium and/or Niobium with Carbon and/or Boron content. Additionally, the presence of coarse chromium carbides is drastically decreased to reduce the amount of check-cracking. Preferably, the weld deposit is produced from a flux-cored or metal-cored wire. The weld deposit characteristics include a matrix having a fine grain size, small evenly dispersed carbides within the matrix, and a small amount of Carbon in the matrix.

FIELD

The present disclosure relates to alloy compositions for arc welding andmore particularly to weld deposit compositions suitable for hardsurfacing that reduce cracking and increase wear resistance andhardness.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Hard-facing relates generally to techniques or methods of applying ahard, wear resistant alloy to the surface of a substrate, such as asofter metal, to reduce wear caused by abrasion, erosion, corrosion, andheat, among other operational or environmental conditions. A variety ofmethods are available to apply the wear resistant alloy to thesubstrate, among which includes welding, where a welding wire isdeposited over the substrate surface to produce a weld deposit that ishighly wear resistant. The welding wire may include a solid wire,metal-cored wire or a flux-cored wire, wherein the metal-cored wiregenerally comprises a metal sheath filled with a powdered metal alloyand the flux-cored wire generally comprises a mixture of powdered metaland fluxing ingredients. Accordingly, flux-cored and metal-cored wiresoffer additional versatility due to the wide variety of alloys that canbe included within the powdered metal core in addition to the alloycontent provided by the sheath.

One known welding wire material that is commonly used for hard-facingincludes chromium carbides. While conventional chromium carbides providegood wear resistance, the weld deposits produced from chromium carbidewelding wires can produce a cross-checking pattern in the hard welddeposit surface, which is undesirable due to an increased susceptibilityto cracking from such patterns. Additionally, coarse chromium carbidescontribute to check-cracking, which are cracks that developperpendicular to a bead direction and accelerate abrasive wear.

SUMMARY

In general, weld deposits with improved crack resistance, improved wearresistance, and improved hardness are provided by using nucleation sitesto control matrix grain size and by balancing Titanium and/or Niobiumwith Carbon and/or Boron content. Additionally, the presence of coarsechromium carbides is drastically decreased to reduce the amount ofcheck-cracking. Preferably, the weld deposit is produced from aflux-cored/metal-cored wire, however, it should be understood that othertypes of welding consumables such as a solid wires or coated shieldedmetal arc electrodes may also be employed. The weld depositcharacteristics include a matrix having a fine grain size, small evenlydispersed carbides within the matrix, and a small amount of Carbon inthe matrix. Additional alloying elements are provided for desiredproperties of the weld deposit and are described in greater detailherein.

In one form of the present disclosure, a weld deposit compositionproduced from a flux-cored or metal-cored welding wire is provided thatcomprises, by percent mass, between approximately 0.7% and approximately2.0% Carbon, between approximately 0.2% and approximately 0.5%Manganese, between approximately 0.5% and approximately 1.1% Silicon,between approximately 2.0% and approximately 8.0% Chromium, betweenapproximately 2.0% and approximately 6.0% Molybdenum, betweenapproximately 2.0% and approximately 5.0% Tungsten, betweenapproximately 2.0% and approximately 8.0% Niobium and Titanium, betweenapproximately 1.0% and approximately 2.5% Vanadium, betweenapproximately 0.2% and approximately 0.9% Boron, and a balancecomprising Iron. In additional forms, the Carbon comprises approximately1.1%, the Manganese comprises approximately 0.3%, the Silicon comprisesapproximately 0.8%, the Chromium comprises approximately 4.0%, theMolybdenum comprises approximately 4.0%, the Tungsten comprisesapproximately 3.5%, the Niobium and Titanium comprise approximately3.2%, the Vanadium comprises approximately 1.8%, and the Boron comprisesapproximately 0.5%.

In another form, a weld deposit composition produced from a flux-coredor metal-cored welding wire is provided that comprises, by percent mass,between approximately 0.7% and approximately 2.0% Carbon, betweenapproximately 0.1% and approximately 0.5% Manganese, betweenapproximately 0.7% and approximately 1.4% Silicon, between approximately6.0% and approximately 11.0% Chromium, between approximately 0.5% andapproximately 2.0% Molybdenum, between approximately 2.0% andapproximately 8.0% Niobium and Titanium, between approximately 0.2% andapproximately 1.0% Vanadium, between approximately 0.2% andapproximately 0.9% Boron, between approximately 0.4% and approximately0.8% Copper, and a balance comprising Iron. In additional forms, theCarbon comprises approximately 1.1%, the Manganese comprisesapproximately 0.3%, the Silicon comprises approximately 0.8%, theChromium comprises approximately 9.0%, the Molybdenum comprisesapproximately 0.8%, the Niobium and Titanium comprise approximately3.5%, the Vanadium comprises approximately 0.3%, the Boron comprisesapproximately 0.5%, and the Copper comprises approximately 0.6%.

In yet other forms of the present disclosure, a flux-cored ormetal-cored welding wire capable of producing a weld deposit having theabove-mentioned elements and a welded structure having a weld depositwith the above elements is provided by the teachings of the presentdisclosure.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a cross-sectional view of a flux-cored or metal-cored weldingwire constructed in accordance with the principles of the presentdisclosure;

FIG. 2 is a perspective view of a welded structure having a hard-facingsurface constructed in accordance with the principles of the presentdisclosure;

FIG. 3 is a chart illustrating test results of compositions inaccordance with the present disclosure compared with prior artcompositions;

FIG. 4 is a photomicrograph of a prior art chromium carbide weld deposithaving a matrix with coarse chromium carbides;

FIG. 5 a is a photomicrograph of a weld deposit exhibiting a matrixhaving a fine grain size in accordance with the teachings of the presentdisclosure; and

FIG. 5 b is a photomicrograph of a second weld deposit exhibiting amatrix having a fine grain size in accordance with the teachings of thepresent disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Weld deposits for use in hard-surfacing applications that produceimproved crack resistance, improved wear resistance, and improvedhardness are provided by controlling matrix grain size and balancingTitanium and/or Niobium with Carbon content according to the teachingsof the present disclosure. Additionally, the presence of coarse chromiumcarbides is drastically reduced to reduce the amount of check-cracking.Preferably, the weld deposit is produced from a flux-cored wire,however, it should be understood that other types of welding consumablessuch as a solid wire or coated shielded metal arc electrodes may also beemployed while remaining within the scope of the present disclosure. Theweld deposit characteristics include a matrix having a fine grain size,small evenly dispersed carbides within the matrix, and a small amount ofCarbon in the matrix. Additional alloying elements are provided forvarious properties of the weld deposit and are described in greaterdetail below.

Referring to FIG. 1, a flux-cored or metal-cored welding wire capable ofproducing weld deposits according to the teachings of the presentdisclosure is illustrated and generally indicated by reference numeral10. The flux-cored/metal-cored welding wire 10 includes a mild steelsheath 12 that is filled with a powdered metal alloy core 14. As shownin FIG. 2, the flux-cored/metal-cored welding wire 10 produces ahard-facing surface 20 when welded onto a substrate 22, to produce awelded structure 24 having improved crack resistance, wear resistance,and hardness.

The specific alloy elements and their amounts that are present in theweld deposits according to the teachings of the present disclosure arenow described in greater detail.

Referring to Table 1 below, two (2) weld deposit compositions (includingboth target percentages and ranges of percent elements by weight)according to the present disclosure are listed as “Weld Deposit A” and“Weld Deposit B,” along with typical M7 tool steel and martensitichard-facing compositions for purposes of comparison. The M7 tool steelis a composition that is used quite frequently in applications involvingsignificant wear and impact. With the compositional modifications tothis M7 tool steel composition made with Weld Deposit A, there issignificant improvement in the wear resistance. The martensitichardfacing composition is a lower cost overlay that has significantusage in the hard-facing industry in applications requiring moderateresistance to wear and impact. Weld Deposit B is a modification of thismartensitic hardfacing composition that results in a significantimprovement in wear resistance. TABLE 1 Weld M7 Deposit Weld MartensiticWeld Weld Tool A Deposit A Hard Deposit Deposit Steel Target RangeFacing B Target B Range C 0.9 1.1 0.7-2.0 0.6 1.1 0.7-2.0 Mn 0.4 0.30.2-0.5 1.5 0.2 0.1-0.5 Si 0.8 0.8 0.5-1.1 1.3 1.0 0.7-1.4 Cr 3.5 4.02.0-8.0 6.0 9.0  6.0-11.0 Mo 8.0 4.0 2.0-6.0 0.7 0.8 0.5-2.0 W 1.5 3.52.0-5.0 0 0 0 Fe Bal Bal Bal Bal Bal Bal Nb, 0 3.2 2.0-8.0 0 3.5 2.0-8.0Ti V 1.6 1.8 1.0-2.5 0 0.3 0.2-1.0 B 0 0.5 0.2-0.9 0 0.5 0.2-0.9 Cu 0 00 0 0.6 0.4-0.8

Each element and its contribution to properties of the weld deposit arenow described in greater detail.

Carbon (C) is an element that improves hardness and strength. Thepreferred amount of Carbon for both Weld Deposit A and Weld Deposit B isbetween approximately 0.7 and 2.0 percent, with a target value ofapproximately 1.1%.

Manganese (Mn) is an element that improves hardness, toughness and actsas a deoxidizer, in which the deoxidizer also acts as a grain refinerwhen fine oxides are not floated out of the metal or if the final grainboundary area is increased by final solidification of amanganese-silicon rich eutectic phase. The preferred amount of manganesefor Weld Deposit A is between approximately 0.2 and 0.5 percent, with atarget value of approximately 0.3%. The preferred amount of manganesefor Weld Deposit B is between approximately 0.1 and 0.5 percent, with atarget value of approximately 0.2%.

Silicon (Si) is an element that acts as a deoxidizer to improvecorrosion resistance and which also acts as a grain refiner when fineoxides are not floated out of the metal or if the final grain boundaryarea is increased by final solidification of a manganese-silicon richeutectic phase. The preferred amount of Silicon for Weld Deposit A isbetween approximately 0.5 and 1.1 percent, with a target value ofapproximately 0.8%. The preferred amount of Silicon for Weld Deposit Bis between approximately 0.7 and 1.4 percent, with a target value ofapproximately 1.0%. Silicon is also added to the weld metal to improvefluidity.

Chromium (Cr) is an element that provides depth of hardenability,corrosion resistance, carbide/boride formation, and improved hightemperature creep strength. The preferred amount of Chromium for WeldDeposit A is between approximately 2.0 and approximately 8.0 percent,with a target value of approximately 4.0%. The preferred amount ofChromium for Weld Deposit B is between approximately 6.0 andapproximately 11.0 percent, with a target value of approximately 9.0%.

Molybdenum (Mo) is an element that provides improved tensile strength ofthe weld deposit as carbide, boride, or a solid-solution strengthener.Tungsten and molybdenum act as solid-solution strengtheners. Tungstenand molybdenum can be substituted for each other in many cases, but themolybdenum is more effective at increasing matrix strength and hardness.The preferred amount of molybdenum for Weld Deposit A is betweenapproximately 2.0 and approximately 6.0 percent, with a target value ofapproximately 4.0%. The preferred amount of molybdenum for Weld DepositB is between approximately 0.1 and approximately 2.0 percent, with atarget value of approximately 0.8%.

Tungsten (W) is an element that provides improved creep strength of theweld deposit. The preferred amount of tungsten for Weld Deposit A isbetween approximately 2.0 and approximately 5.0 percent, with a targetvalue of approximately 3.5%. Tungsten is not present in Weld Deposit Bdue to cost considerations and the presence of molybdenum.

Titanium (Ti) and Niobium (Nb) act as grain refiners, deoxidizers, andprimary carbide/boride formers. The amounts of Titanium and Niobium arebalanced with the amount of Carbon/Boron as set forth above in order toreduce the amount of Carbon/boron in the weld metal matrix and grainboundaries, which reduces the possibility of cracking and improves thetoughness of the hard-facing surface. The ratios of the elements arebased on the atomic weights and the type of intermetallic carbide/boridedesired. The Titanium is generally 4 times the mass of Carbon, and theniobium is generally 8 times the mass of Carbon. Any excess Carbon isleft to the secondary carbide formers and the matrix. The ratio of theTitanium to Boron is 4.4 for Titanium Boride and 2.2 for TitaniumDiboride. The Niobium/Boron ratio is 8.6 for Niobium Boride and 4.3 forNiobium Diboride. The Titanium/Niobium and the Carbon/Boron pairs aresubstitutional in nature, and thus deviations from these ratios can betolerated and should be construed as falling within the scope of thepresent disclosure. Additionally, particles of these elements freeze ata very high temperature and are therefore considered primarycarbides/borides.

Vanadium (V) is secondary carbide former and a grain refiner and thusincreases toughness of the weld deposit. The preferred amount ofVanadium for Weld Deposit A is between approximately 1.0 andapproximately 2.5 percent, with a target value of approximately 1.8%.The preferred amount of Vanadium for Weld Deposit B is betweenapproximately 0.2 and approximately 1.0 percent, with a target value ofapproximately 0.3%.

The Titanium and Niobium when combined with Carbon and/or Boron will actas grain refiners to provide nucleation sites for the formation of manysmall grains, which contribute to improved crack resistance.Additionally, the small grains improve ductility and reduce hot tearingby increasing the grain boundary area and reducing the average distancethat the grains have to slide against each other to accommodate thelocal strain induced by shrinkage due to cooling. The grain boundarysliding is known as shear, which is generally responsible forhot-tearing in the grain boundaries.

Boron (B) is an element that provides interstitial hardening in thematrix, strengthens the grain boundaries by accommodating mismatches dueto incident lattice angles of neighboring grains with respect to thecommon grain boundary, and by itself or in combination with Carbon, formnucleation sites as intermetallics with Titanium and/or Niobium. Thepreferred amount of Boron for Weld Deposit A is between approximately0.2 and approximately 0.9 percent, with a target value of approximately0.5%. The preferred amount of Boron for Weld Deposit B is betweenapproximately 0.2 and approximately 0.9 percent, with a target value ofapproximately 0.5%.

Copper (Cu) is an alloying element that can be used in steels to modifythe structure by providing a secondary phase to partition/refine grainsor by depressing the freezing point of the austenite phase for a shorterfreezing range. The shorter freezing range means that less shear strainis exerted on the phase due to the coefficient of thermalexpansion/contraction. In effect, there is less strain due to thecontraction that occurs upon cooling because the austenite is cooledthrough only half of its normal freezing range. Since austenite is proneto hot tearing, targeting this phase to avoid any excess shear stressesgreatly reduces this failure mechanism in the alloy. The preferredamount of Copper for Weld Deposit B is between approximately 0.4% andapproximately 0.8%, with a target value of approximately 0.6%.Preferably, there is no Copper in Weld Deposit A.

The compositions of the weld deposits according to the teachings of thepresent disclosure are formulated to reduce the amount of cross-checkingas compared with other martensitic and tool steel welding wire depositswhile improving wear resistance. In exemplary testing, the compositionof Weld Deposit A has shown improved hardness and weight loss whencompared to other weld deposit compositions as shown below in Table 2.TABLE 2 ASTM HRC G-65 Wear Test Composition Hardness Value Weight LossWeld Deposit A HRC 62 to 67 0.13 grams Typical Chromium Carbide HRC 55to 63 0.15 grams M7 Tool Steel HRC 60 to 64 0.55 grams MartensiticDeposit HRC 58 to 60 1.30 grams Weld Deposit B HRC 63-65 0.21 grams

Referring to FIG. 3, the wear resistance of the compositions of thepresent disclosure and those from prior art are illustrated. Comparingprior art alloys, the chromium carbide hard-facing has been seen to havethe best wear resistance (lowest weight loss in the ASTM G65 wear test).However, the chromium carbide deposit contains relief check-cracks thatmake the overlay less suitable for applications that involve both highimpact and wear. With the composition according to Weld Deposit A, wearresistance is enhanced to be better than that of the chromium carbidedeposit and the M7 Tool Steel as shown. Similarly, the compositionaccording to Weld Deposit B results in significantly better wearresistance than the Martensitic deposit. Therefore, Weld Deposit B ishighly suitable in applications involving moderate impact and abrasionwith only marginal increase in cost over the Martensitic deposit.

By controlling the matrix grain size and balancing the Titanium and/orNiobium with the Carbon/Boron content, weld deposits having improvedcrack resistance are produced according to the teachings of the presentdisclosure. Additionally, the weld deposits according to the presentdisclosure do not contain coarse chromium carbides. The absence of thecoarse chromium carbide phases will reduce the presence ofcheck-cracking.

By way of example, FIG. 4 illustrates a prior art weld deposit matrixhaving coarse chromium carbides, and FIGS. 5 a and 5 b illustrate theweld deposit matrices according to the present disclosure without suchcoarse chromium carbides. As shown, the exemplary weld deposits of thepresent disclosure exhibits a fine grain size within the matrix,combined with small and evenly dispersed carbides. The fine grain sizeand evenly dispersed carbides contribute to improved crack resistanceand improved wear resistance.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the gist of the disclosure areintended to be within the scope of the disclosure. For example, the welddeposit according to the teachings of the present disclosure may beproduced from welding wire types other than flux-cored/metal-coredwires, such as solid wires, while remaining within the scope of thepresent disclosure. Such variations are not to be regarded as adeparture from the spirit and scope of the disclosure.

1. A weld deposit composition produced from a flux-cored or metal-cored welding wire comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.2% and approximately 0.5% Manganese; between approximately 0.5% and approximately 1.1% Silicon; between approximately 2.0% and approximately 8.0% Chromium; between approximately 2.0% and approximately 6.0% Molybdenum; between approximately 2.0% and approximately 5.0% Tungsten; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 1.0% and approximately 2.5% Vanadium; between approximately 0.2% and approximately 0.9% Boron; and a balance comprising Iron.
 2. The weld deposit composition according to claim 1, wherein the Carbon comprises approximately 1.1%.
 3. The weld deposit composition according to claim 1, wherein the Manganese comprises approximately 0.3%.
 4. The weld deposit composition according to claim 1, wherein the Silicon comprises approximately 0.8%.
 5. The weld deposit composition according to claim 1, wherein the Chromium comprises approximately 4.0%.
 6. The weld deposit composition according to claim 1, wherein the Molybdenum comprises approximately 4.0%.
 7. The weld deposit composition according to claim 1, wherein the Tungsten comprises approximately 3.5%.
 8. The weld deposit composition according to claim 1, wherein the Niobium and Titanium comprise approximately 3.2%.
 9. The weld deposit composition according to claim 1, wherein the Vanadium comprises approximately 1.8%.
 10. The weld deposit composition according to claim 1, wherein the Boron comprises approximately 0.5%.
 11. A weld deposit composition produced from a flux-cored welding wire comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.1% and approximately 0.5% Manganese; between approximately 0.7% and approximately 1.4% Silicon; between approximately 6.0% and approximately 11.0% Chromium; between approximately 0.5% and approximately 2.0% Molybdenum; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 0.2% and approximately 1.0% Vanadium; between approximately 0.2% and approximately 0.9% Boron; between approximately 0.4% and approximately 0.8% Copper; and a balance comprising Iron.
 12. The weld deposit composition according to claim 11, wherein the Carbon comprises approximately 1.1%.
 13. The weld deposit composition according to claim 11, wherein the Manganese comprises approximately 0.3%.
 14. The weld deposit composition according to claim 11, wherein the Silicon comprises approximately 0.8%.
 15. The weld deposit composition according to claim 11, wherein the Chromium comprises approximately 9.0%.
 16. The weld deposit composition according to claim 11, wherein the Molybdenum comprises approximately 0.8%.
 17. The weld deposit composition according to claim 11, wherein the Niobium and Titanium comprise approximately 3.5%.
 18. The weld deposit composition according to claim 11, wherein the Vanadium comprises approximately 0.3%.
 19. The weld deposit composition according to claim 11, wherein the Boron comprises approximately 0.5%.
 20. The weld deposit composition according to claim 11, wherein the Copper comprises approximately 0.6%.
 21. A flux-cored welding wire capable of producing a weld deposit composition comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.2% and approximately 0.5% Manganese; between approximately 0.5% and approximately 1.1% Silicon; between approximately 2.0% and approximately 8.0% Chromium; between approximately 2.0% and approximately 6.0% Molybdenum; between approximately 2.0% and approximately 5.0% Tungsten; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 1.0% and approximately 2.5% Vanadium; between approximately 0.2% and approximately 0.9% Boron; and a balance comprising Iron.
 22. A flux-cored welding wire capable of producing a weld deposit composition comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.1% and approximately 0.5% Manganese; between approximately 0.7% and approximately 1.4% Silicon; between approximately 6.0% and approximately 11.0% Chromium; between approximately 0.5% and approximately 2.0% Molybdenum; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 0.2% and approximately 1.0% Vanadium; between approximately 0.2% and approximately 0.9% Boron; between approximately 0.4% and approximately 0.8% Copper; and a balance comprising Iron.
 23. A welded structure comprising at least one weld deposit, the weld deposit having a composition comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.2% and approximately 0.5% Manganese; between approximately 0.5% and approximately 1.1% Silicon; between approximately 2.0% and approximately 8.0% Chromium; between approximately 2.0% and approximately 6.0% Molybdenum; between approximately 2.0% and approximately 5.0% Tungsten; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 1.0% and approximately 2.5% Vanadium; between approximately 0.2% and approximately 0.9% Boron; and a balance comprising Iron.
 24. A welded structure comprising at least one weld deposit, the weld deposit having a composition comprising, by percent mass: between approximately 0.7% and approximately 2.0% Carbon; between approximately 0.1% and approximately 0.5% Manganese; between approximately 0.7% and approximately 1.4% Silicon; between approximately 6.0% and approximately 11.0% Chromium; between approximately 0.5% and approximately 2.0% Molybdenum; between approximately 2.0% and approximately 8.0% Niobium and Titanium; between approximately 0.2% and approximately 1.0% Vanadium; between approximately 0.2% and approximately 0.9% Boron; between approximately 0.4% and approximately 0.8% Copper; and a balance comprising Iron. 